Assessing Greenhouse Gas Emissions Mitigation Potential through the use of Forest Bioenergy
Bioenergy production from forest resources offers opportunities to reduce greenhouse gas (GHG) emissions associated with fossil fuel use, reduce non-renewable energy consumption, and provide investment and employment in the forestry sector. These opportunities, however, must be considered within the broader contexts of forest systems. Of particular interest is how bioenergy opportunities impact carbon storage within the forest. This thesis develops a method to integrate life cycle assessment and forest carbon analysis approaches to quantify the total GHG emissions associated with forest bioenergy. Bioenergy production and utilization decisions are then investigated to evaluate opportunities to increase GHG mitigation performance. An accounting method is developed to evaluate the impact of emissions timing on the cost-effectiveness of GHG emissions reductions from biomass-based electricity generation. Applying the integrated life cycle assessment/forest carbon analysis method to a case study of forest bioenergy production in Ontario reveals significant reductions in forest carbon associated with bioenergy production. Wood pellet production from standing trees or harvest residues (displacing coal in electricity generation) would increase total GHG emissions over periods of approximately 40 and 15 years, respectively. Ethanol production (displacing gasoline) would increase GHG emissions throughout the 100-year model period if produced from standing trees; emissions would increase over a period of approximately75 years if produced from harvest residues. Strategic ethanol production decisions (e.g., process energy source, co-location with other processes, co-product selection) can improve GHG mitigation. Co-production of biomass pellets with ethanol performs best among co-product options in terms of GHG emissions; co-location with facilities exporting excess steam and biomass-based electricity further increases GHG mitigation performance. Delayed GHG reductions due to forest carbon impacts the cost of GHG emissions reductions associated with electricity production from forest biomass. Cost-effectiveness is heavily dependent on the time horizon over which global warming impacts are measured and influences the ranking of biomass electricity pathways (biomass co-firing is the most cost-effective pathway between 2020 and 2100; biomass cogeneration is the most cost-effective pathway beyond year 2100). The accounting tools and methods developed within this thesis will to help inform decision-makers in the responsible development of forest bioenergy opportunities and associated policies.
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